Step 1

Heat oven to 350°F.

Step 2

Line 13x9-inch pan with foil, with ends of foil extending over sides; spray with cooking spray.

Step 3

Microwave unsweetened chocolate and butter in large microwaveable bowl on HIGH 2 min. or until butter is melted. Stir until chocolate is completely melted. Add sugar; mix well. Blend in eggs. Add flour; mix well. Stir in nuts. Spread into prepared pan.

Step 4

Bake 30 to 35 min. or until toothpick inserted in center comes out with fudgy crumbs. (Do not overbake.) Meanwhile, microwave caramels and milk in microwaveable bowl on HIGH 2-1/2 min., stirring after 1 min. Stir until caramels are completely melted and mixture is well blended.

Step 5

Spread caramel sauce over brownie; cool 5 min. Sprinkle with chocolate chunks. Cool completely. Use foil handles to lift brownies from pan before cutting to serve.